Ultrasound devices are now well established as tools for a variety of medical diagnoses. One of the widely used clinical ultrasound imaging systems is Doppler processing system, which enables a user to make estimates of blood velocity in various vessels of a patient's body by extracting the Doppler shift from returned echo signals reflected off of blood cells. Doppler ultrasound techniques and apparatus thus offer a convenient and non-invasive means for diagnosing various conditions related to blood flow velocity in different parts of human body.
One of such conditions capable of being determined ultrasonically is the intracranial pressure. The measurement of intracranial pressure (ICP) is important in diagnosing and treating various pathophysiological conditions caused by head trauma, hemorrhage, tumors, inflammatory diseases and the like. A few methods and techniques have been proposed for non-invasive assessment of intracranial pressure. One such method is described in U.S. Pat. No. 5,951,477 to Ragauskas et al., which comprises steps of using an ultrasound Doppler device to detect the velocities of the blood flow inside the ophthalmic artery for both intra-cranial and extra-cranial ophthalmic artery portions and applying a small pressure to the eye of a patient, sufficient enough to equalize the blood flow measurements of the internal and external portions of the ophthalmic artery. The pressure at which such equalization occurs is found to be an acceptable indication of the intracranial pressure.
Although the above method of using the ultrasound equipment to measure the intracranial pressure has been in use for a number of years, there is still a need for test equipment which can simulate human arterial flow, permit detailed hemodynamic measurements, and allow clinical-type ultrasound examinations.
A number of attempts have been made in the past to provide effective diagnostic devices that mimic blood flows and systolic movement of vessels within the human body. One such device disclosed in U.S. Pat. No. 5,560,242, issued to Flax, comprises an open-cell foam material matrix having a first density and a movable belt having a second density. The belt rotates on pulleys to simulate blood flow. In another embodiment the belt is replaced by a rotating disk of the same material as the belt such that differing blood flow rates between adjacent blood vessels can be simulated for ultrasonic imaging. However, there are several disadvantages associated with this type of phantom device. One of such disadvantages is that the scattering signals reflected off the belt are too ideal and do not indicate how the ultrasound system will operate under more realistic conditions.
Another type of blood flow device utilizes blood mimicking fluid flow through tubes to simulate blood flow within the human body. The blood mimicking fluid contains a scatter material with reflects sonic waves similarly to the way blood platelets reflect ultrasonic waves in blood. For example, U.S. Pat. No. 6,595,923 to Sjoblom discloses one such device comprising a tissue-mimicking material containing a plurality of fluid flow path through which fluid is pumped. The fluid flow paths are made of tubing and each extends over a different portion of the depth of the device and at a different angle, thus simulating blood vessels located at various depths within the human body. One of the problems with such device is that it is incapable of producing a flow of blood mimicking fluid with a physiologically correct pressure and flow distribution data, as it only produces a flow of constant character and constant pressure.
U.S. Pat. No. 5,052,934, issued to Carey, et al., discloses a device for evaluation of prosthetic valves and cardiac ultrasound procedures, wherein a controlled pulsatile flow of a blood mimicking fluid is passed through a multi-chambered region into which are mounted mitral and aortic valves and adjustably positioned ultrasound transducers. Although such device is capable of producing a pulsatile flow, thus assuring a uniform distribution of scatter material in the blood mimicking fluid and providing more accurate flow rates over a wide range of flow velocities, because of its specific design it is clearly limited to clinical evaluation of cardiac ultrasound procedures and is not suitable for evaluation of ultrasound devices used to detect the velocities of the blood flow inside the human ophthalmic artery.
Therefore, none of the above-shown systems are able to produce flows of a blood simulating fluid that have characteristics equivalent to those of blood flow in the intra-cranial and extra-cranial segments of human ophthalmic artery.